Polarity device



1941- H. E. coRBrrr POLARITY DEVICE Original Filed Jan. 27, 1959,

2 Shee'ts-Sheet 1 a ma W m w I a T MmW 1 3 EN r Q M Dec. 30, 1941. H. E.coRBrrT 2,268,375

POLARITY DEVICE Original Filed Jan. 27, 1939 2 Sheets-Sheet 2 CURRENTFLOW CURRENT FLO W I f E 5 26 3 2 7 INVENTOR. H0 WHRD E. CORBITT BY $.QM

ATTORNEY Patented Dec. 30, 1941 POLARITY DEVICE Howard E. Corbitt,Alhambra, Calii'., asslgnor to Percy E. Landolt, New York, N. Y., astrustee Original application January 27,

253,125. Divided and this application June 23 1941, Serial No. 399,383

7 Claims.

The present invention relates to polarity devices, and, moreparticularly, to a polarity device of novel and improved characteradapted for operation in connection with an electrical precipitatorsystem.

As those skilled in the art know, in electrical precipitator systemshigh unidirectional voltages are employed which are generally obtainedby stepping-up the voltage of an alternating current source by means ofa transformer and then rectifying the high alternating current potentialby means of a rotary rectifier driven by means of a synchronous motorsupplied with current from the same alternating current source. In orderto provide the proper polarity of the unidirectional or rectifiedvoltage on the precipitator electrodes, it was necessary to obtain apredetermined phase relationship between the rotation of the motor andthe voltage of the alternating current source. In practical operation itfrequently happened that after the motor reached synchronous speed, theunidirectional voltage obtained from the rectifier had the opposite orwrong polarity. According to prior practice, this condition wascorrected by disconnecting the synchronous motor for a time sufficientto let the rotor slip back by 180 (electrical) whereby the desired andproper polarity was obtained. Of course, this procedure causedinconvenience and considerable loss of time as frequently severalattempts were necessary before the proper polarity was obtained.

It was already suggested to provide automatic devices for obtaining thedesired and proper polarity of the rectified voltage by automaticallyeffecting connection of the synchronous motor to the source of currentor its temporary disconnection from the source of current in the desiredand proper sequence. All of these prior devices, however, involved theapplication of relatively complex circuits and included commutators orsliding contacts cooperating with the synchronous motor. Experience hasdemonstrated that these devices frequently suffered from operatingdifliculties and especially the rotary contacts were a constant sourceof trouble and required frequent replacements. Although also variousother suggestions and proposals were made to solve the outstandingproblem and to provide a polarity device of completely satisfactorycharacter, none of these suggestions or proposals was completelysatisfactory or successful on a practical and industrial scale.

I have discovered a novel polarity device which completely eliminatesall of the difliculties and 1939, Serial No.

inconveniences connected with the construction and operation ofconventional devices.

It is another object of the present invention to provide a polaritydevice which relies for its operation on closing and opening of amagnetic circuit operatively associated with the synchronous motor ofthe rotary rectifier and which is completely free from rotary contacts,brushes and other sources of operating difliculties.

It is a further object of the invention to provide a polarity devicewhich may be mounted on the frame of the synchronous motor driving therotary rectifier and which has a stationary portion and a rotaryportion, the rotary portion being free from current conducting elementsthereby avoiding the necessity for contact rings, brushes, and the like.

The invention also contemplates a polarity device adapted to be mountedon the synchronous motor driving a rotary rectifier and having anelectrical system connected therewith capable of effecting connection ofthe source of alternating current to the step-up transformer in theproper time relationship thereby to automatically obtain the desired andproper polarity of the high unidirectional voltage on the precipitatorelectrodes.

The invention also contemplates a polarity device and an electricalsystem associated therewith which is simple in character, positive andfoolproof in operation and which may be readily manufactured and used onan industrial scale at a low cost.

Other and further objects of the invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

Fig. 1 illustrates a side elevational view having parts in section ofthe polarity device embodying the present invention;

Fig. 2 depicts one of the laminations employed in the rotor of thepolarity device;

Fig. 3 shows a front elevation of the stator frame assembly of thepolarity device;

Figs. 4 and 5 show two possible wave forms that may be obtained with thepolarity device when it is operating as shown in the wiring diagram ofFig. 6; and

Fig. 6 is a complete wiring diagram of the polarity device embodying theinvention.

Broadly stated, according to the principles of my invention, I provide amagnetic circuit having a stationary portion adapted to be mounted onthe frame of the synchronous motor driving a rotary rectifier and havinga rotary portion rigidly connected to the shaft of the synchronousmotor, and adapted to periodically close a gap in the magnetic circuitduring rotation of said motor. The effect of the rotation of thesynchronous motor on this magnetic circuitwill be to complete it and tosubstantially interrupt the same, or to increase its resistance to asubstantial extent, a predetermined number of times per second,dependent upon the speed of rotation of the synchronous motor. Incooperation with this magnetic circuit, I provide stationary primary andsecondary coils which are exposed to the effect of the variations in themagnetic flux present in the circuit. The primary coil is supplied withunidirectional and pulsating current derived from the alternatingcurrent source of the synchronous motor through a half-wave rectifier.The secondary coils are connected to the electrical system proper andare capable to cause the actuation of a relay, provided the currentinduced therein reaches at least a predetermined minimum value.

During rotation of the synchronous motor, the resistance in the magneticcircuit will periodically vary, as a result of the opening and closingof the gap in said circuit by the rotary portion thereof. Generallyspeaking, it is possible that each time when the pulsating current inthe primary coil obtains its maximum value, the magnetic system has itsminimum of resistance, or vice versa. Accordingly, the amount of currentflowing in the secondary coil, or coils may be of a substantial value orof a relatively low value, dependent upon the phase relationship betweenthe alternating current and the polarity of the direct current impulsesderived from the half-wave rectifier. In the first case, a, relayoperatively associated with the secondary coils may be actuated and maycause interruption and reclosing of the main circuit of the synchronousmotor within a predetermined time interval and thereby can re-establishthe proper polarity of the output of the rotary rectifier as it will beexplained more fully hereinafter.

Referring now more particularly to the drawings, Fig. 1 illustrates aside elevational view having parts in section of a polarity deviceembodying the principles of the present invention and drawn toapproximately full scale. Reference character 4 denotes the laminatediron stator which is attached to the end frame of rectifier motor 9 bymeans of a brass casting I; I denotes the laminated iron rotor attachedto a brass casting II and held in position by means of clip I2 and ascrew associated therewith. Around stator frame 4 at about its mid-pointis provided a primary coil 1 having its terminals connected to a sourceof alternating current through a resistor and a half-wave rectifier.Also around the stator frame 4 are provided two secondary coils 8 beingpositioned as close to air gap 6 as practicable. These secondary coilsare connected in series and their terminals are connected to theoperating coil of a single-pole re-' lay. In Fig. 1, rotor I is shown inthe position which presents a minimum air gap 6. If the rotor l wasrotating synchronously in this position and at this synchronous time thehalfwave rectifier permitted current to pass through coil I, then coils8 would present their maximum potential to the terminals of theoperating relay above mentioned. I3 is the rectifier motor shaft and I4denotes set screws for attaching member I I to said shaft.

The shape of the laminations employed in the polarity device will bebest seen in Figs. 2 and 3.

Of these, Fig. 2 shows a front elevation of one lamination of the ironrotor of the polarity device, reference character I denoting thelamination itself. Lamination I is provided with four ears 2 projectingoutwardly in such a manner that a casting may be attached to the centralbody of the assembled laminations. Rivet holes 3 are provided in thelaminations for connecting them into a rigid and unitary structure. Fig.3 shows a, front elevational view of the stator lamination iron frameafter assembly and as it would appear when viewed from the end of therectifier motor. Reference character 4 denotes the stator assembly, andreference character 5 denotes the four outermost laminations, theextensions of which are bent back as shown by the dotted lines after thecoils are slipped in place.

The operation of the polarity device embodying the present inventionwill be best understood from Fig. 6. Reference character 22 denotes ahigh voltage transformer, the secondary winding of which is connected toa mechanical rectifier 23, the rectified high voltage current beingsupplied to a precipitator 24. The primary winding of high voltagetransformer 22 is connected to leads 25 and 26 of a source ofthree-phase alternating current 25, 26 and 21. The mechanical rectifieris driven by means of a 4-pole, three-phase squirrel cage inductionmotor 28 having slots cut in its iron rotor to simulate a 4-polemachine, this motor starting as an induction motor and running as asynchronous motor having no brushes, or separate excitation. Obviously,motor 28 may come up to synchronous speed in two positions with respectto mechanical rectifier 23 which is mounted directly on the shaft of therotor of motor 28. Thus, assuming that the rotor of mechanical rectifier23 has a certain point thereon synchronously opposite to the stator shoeconnected to ground 29, when a change of 180 mechanical degrees wouldnot change the polarity of 29. A change of 90 mechanical degrees,however, in either direction would change the polarity of ground 29. Inother words, motor 28 may come up to synchronous speed so that ground 29ispositive, and it also may come up to speed so that ground would be ofthe opposite polarity, or negative. Normal precipitation requires thatground 29 be positive. The circuit and associated devicesshown in Fig. 6are of such character that the ground may be automatically maintained atpreferred and pre-selected polarity and that this selection may beobtained before transformer 22 is connected to the power line, withoutrequiring any brushes or similar frictional devices on motor 28.

One phase of the power supply, lead 21, is directly connected to onelead of three-phase rectifier motor 28. The other two leads 25 and 26are connected to the remaining two leads of rectifier motor 28 through atwo-pole magnetic switch 30. A start push button 3I of the momentarymake type and a stop push button of the momentary break type 32 areprovided. The circuit also includes an auxiliary relay 33 which is asingle-pole, open when de-energized, magnetically operated switch, and apolarity device relay 34 which is a single-pole, closed whendeenergized, magnetically operated switch. The polarity selector deviceproper comprises an iron stator 4 mounted on the end frame of rectifiermotor 28; and an ironrotor I attached directly to the rotor of therectifier motor 28 as indicat-ed by dotted line 35. Rotor I is sopositioned as to form part of the magnetic circuit of stator 4. Onstator 4 is wound a primary coil 1 and close to the air gaps betweenrotor and stator, but around the stator, are wound two secondary coils 8forming a secondary circuit under the transformer action of primarycoil 1. A low voltage tap I8 from one phase of the rectifier motor isconnected to one terminal of primary winding 1, and the other terminalis connected to this low voltage through a half-wave rectifier 2| and aresistor 28. These connections are made on the motor side of motorstarter switch 30 so that this circuit is open when the motor starterswitch is open.

When it is desired to place rectifier motor 28 in operation, push button3| is momentarily depressed. This connects power supply lead 26 throughthe closed contact of push button 32 to one terminal of the operatingcoil 33a of auxiliary relay 33, the other terminal of this operatingcoil being connected to lead of the power supply. This operates relay 33which closes its single-pole contact causing current to flow from powersupply lead 28 through closed contact push button 32, through the nowclosed contact of auxiliary relay 33 to its own operating coil terminaland thence back to power supply lead 25. The auxiliary relay will remainin this position until push button 32 is momentarily opened. Upon suchactuation of relay 33, motor starter switch will be energized asfollows: Current fiows from power supply lead 25 through the operatingcoil 38a of motor starter switch 38, through the closed contacts of thesingle pole polarity device relay 34 and back to power supply lead 26through the now closed contacts of relay 33 and closed contact of pushbutton 32. Thus, the two-pole motor starter switch 30 is actuated andcloses its contacts, applying the three-phase power supply lead 25, 26and 21 to the leads of rectifier motor 28. When the motor is energized,potential is applied to the primary winding of polarity device I througha reduced voltage tap described in the foregoing. The secondary coils ofthis polarity device 8 are connected to the operating coil ofsingle-pole relay 34. As motor 28 reaches synchronous speed, a potentialappears across the operating coil of relay 34 and its magnitude dependsupon the relation between the direction of current flow through thehalf-wave rectifier 2| and the synchronous position occupied by thepolarity device rotor I with respect to its stator 4. Sufficient time isrequired to cause the closed contact 36 of polarity device relay 34 tooperate so that the starting of rectifier motor 28 cannot cause contact36 to operate until synchronous speed is reached. Therefore, onlypotentials applied to operating coil I during synchronous operation ofrectifier motor 28 need be considered.

If the half-wave rectifier 2| permits current to flow at a time whenrotor is in such a position as to provide a minimum air gap in themagnetic circuit of 4 and I, then a large voltage will be applied acrossthe operating coil of relay 34. Relay 34 is so adjusted as to beoperated by this potential, opening single-pole contact 36, thus in turnopening the operating coil circuit of motor starter 30. As soon as thismotor starter 38 opens the circuit of motor 28, the potential is removedfrom the operating coil of polarity device.relay 34. This causes itscontact 36 to close again which in turn energizes motor starter 38 andalso energizes motor 28. When contact 36 of relay 34 is adjusted forproper timing, motor 28 may be removed from power leads 25 and 28rectifier 23 is mechanical degrees earlier or later than that assumed inthe above illustration, and the half-wave rectifier 2| allows current topass synchronously as before, rotor of the polarity device will be insuch synchronous position as to provide a maximum air gap in themagnetic path of stator 4 and rotor I. Of course, it is assumed that themechanical rectifier 23 is maintained in its previous mechanicalrelationship on the shaft of motor 28 with respect to rotor l. A minimumpotential now appears across the terminals of operating relay coilbecause the transformer action of primary coil 1 upon secondary coils 8is greatly decreased due to flux leakage. This potential is insufllcientto operate relay 34, as it may easily be as little as one-third of thepotential required to operate the relay. This is the condition of normaloperation when the polarity of the mechanical rectifier 23 is correctwith respect to the precipitator 24.

Figs. 4 and 5 depict the wave forms obtained from the polarity deviceembodying the present invention and represent two possible synchronouspositions. Reference character l5 in Fig. 4 denotes the wave form whichis sufllcient to operate relay coil while IS in Fig. 5 denotes the waveform which is insufficient to actuate the relay. The circuits shown inFigs. 4 and 5 are identical in all respects, except that the synchronousposition of the rotor is different. Terminals l8 and |9 are connected toa source of alternating current which is connected in series with aresistor 28, with primary coil 1 of the polarity device, and a half-waverectifier 2|. The magnetic circuit of the device is formed by an ironstator 4 and an iron rotor I. In Fig. 4 stator and rotor are shown inthe synchronous position of minimum air gap while the current is passedby rectifier 2| and in Fig. 5 stator and rotor are shown in thesynchronous position of maximum air gap while the current is passed byrectifier 2 Stator 4 carries two secondary polarity device coils 8 whichare connected in series with each other and with a relay coil l1.Reference character 22a indicates the points between which a cathode rayoscillograph was connected to obtain oscillograms l5 and Hi.

It will be noted that the polarity device of the invention providesimportant advantages. First of all, a novel and improved device isprovided which is completely automatic in its operation and does notrely in any way on the competency or skill of the operator. At any timewhen the device is connected, the proper and desired polar-- ity will beobtained on the precipitator electrodes with the complete exclusion oferrors and completely avoiding the danger of improper connections.

It is also to be observed that the polarity device of the invention isextremely simple in construction and due to the complete absence ofsliding contacts, rings or commutators, it is free from the mostimportant source of trouble of prior devices of similar character.

Of course, those skilled in the art will readily appreciate that thedevice of the invention may be applied with equal or similar results toinstallations different from precipitator systems such as, for example,X-ray installations and other systems wherein a high voltage alternatingcurrent is converted into unidirectional current by means of asynchronous rotary rectifier.

Although the present inventionhas been described in connection with apreferred embodiment thereof, variations and modifications may beresorted to by those skilled in the art without departing from theprinciples of the present invention. I consider all of these variationsand modifications as within the true spirit and scope of the presentinvention as disclosed in the foregoing description and defined by theappended claims.

The present application is a division of my pending application SerialNo. 253,125, filed January 27, 1939, now Patent .No. 2,247,361, issuedJuly 1, 1941.

I claim:

1. In an electrical system including a source of alternating current, arotary rectifier driven by a synchronous motor and a load connected tothe output of said rectifier; a polarity selector device comprising incombination an iron stator bearing a primary coil connected to saidsource of alternating current, a half-wave rectifier in series with saidprimary coil, secondary coils mounted on said stator and in the magneticcircuit thereof, a rotor attached to the rotor of said synchronous motorand forming part of said magnetic circuit, and means actuated by thecurrent induced in said secondary coils for conthe time intervals duringwhidir, said stator is energized through said half-wave rectifiercoincide with the intervals when said rotor completes the air gap insaid stator, and means responsive to said strong current impulses forinterrupting the circuit of said synchronous motor for a predeterminedtime interval sufiicient to obtain correction of the polarity of therectified voltag on saidNoad.

4. In a rectifier system including a rotary rec-,

tifier connected to a source of alternating current and a synchronousmotor driving said rectifier, a polarity selector device comprising incombination a magnetic circuit, a primary and a secondary selectorcircuit mounted in cooperative position with said magnetic circuit andin inductive relation with respect to each other, a halfwave rectifierconnected in series with said primary circuit and with said source ofalternating current and adapted to periodically energize said magneticcircuit, a magnetizable element interposed in said magnetic circuit androtated at identical velocity with said synchronous motor adaptedtoperiodically increase the inductive coupling between said primary andsaid secondary circuit to cause induction of current impulses in saidsecondary circuit, and means electrically associated with said secondarycircuit and retrolling the polarity of rectified voltage on said load.

2. In an electrical system including a source of alternating current, arotary rectifier driven by a synchronous motor and a load connected tothe output of said rectifier; a polarity selector device comprising incombination an iron stator mounted on the end frame of said synchronousmotor, a primary coil mounted on an intermediate portion of said statorand a pair of secondary coils mounted on the terminal portions of saidstator, a half-wave rectifier connected in series with said primary coiland with said source of alternating current, an iron rotor directlyattached to the rotor of said synchronous motor forming part of themagnetic circuit of said stator and being adapted to intermittentlycomplete said circuit duringthe rotation thereof, and means actuated bythe current induced in said secondary coils for interrupting the circuitof said synchronous motor for a predetermined time interval sufiicientto obtain correction of r the polarity of the rectified voltage on saidload.

3. In an electrical system including a high voltag transformer connectedto a source of alternating current, a rotary rectifier driven by asynchronous motor and a load connected to the output of said rectifier;a polarity selector device comprising in combination a substantiallyC-shaped iron stator mounted on the end frame of said synchronous motor,a primary coil mounted on the intermediate portion of said stator and apair of secondary coils mounted close to the air gap in said stator, ahalf-wave rect fier connected in series with said primary coil and withsaid source of alternating current and adapted to establish anintermittent magsponsive to predetermined intensities of said impulsesfor controlling the polarity of the output of said rotary rectifier.

5. In a rectifier system including a rotary rectifier connected to asource of alternating current and a synchronous motor driving saidrectifier, a polarity selector device comprising in combination astationary magnetizable member, a rotatable magnetizable member rotatedby said synchronous motor and adapted to periodically form a'substantially closed magnetic circuit with said stationary member,primary and secondary coils mounted on said stationary member ininductive relation with respect to each other, a half-wave rectifierconnected in series with said primary coil and with said source ofalternating current and adapted to periodically energize said magneticcircuit, and means responsive to a predetermined value of currentimpulses induced in said secondary coils for interrupting the circuit ofsaid synchronous motor for a predetermined time interval sufficient tocorrect the polarity of the rectified direct current voltage.

6. In a rectifier system including a rotary rectifier connected to asource of alternating current and a synchronous motor fed from the samesource for driving said rectifier, a polarity selector device comprisingin combination a stationary magnetizable member, a rotatablemagnetizable member rotated bysaid synchronous motor at a speedidentical with that of said motor and adapted to periodicall form asubstantially closed magnetic circuit with said stationary member,primary and secondary coils in inductive relation with each other andwith said magnetic circuit, a half-wave rectifier connected in serieswith said primary coil and with said source of alternating current andadapted to periodically energize said coil and said magnetic circuitwhereby relatively strong current impulses will be induced in saidsecondary coil when the periodical closing of the magnetic circuitcoincides with the periodical energizing of said primary coil andrelatively weak current impulses will be induced in said secondary coilwhen the periodical closing of the magnetic circuit does not coincidewith the periodical energizing of said primary coil, and switching meansresponsive to said strong impulses but unafiected by said weak impulsesfor interrupting the motor circuit for a time interval sufiicient tocorrect the polarity of the rectified direct current voltage.

7. In a rectifier system for producing high unidirectional potentialfrom an industrial low voltage alternating current source including ahighvoltage step-up transformer connected to said source and amechanical rectifier of the rotary spark gap type connected to saidtransformer and driven by a synchronous motor fed from the same source;a polarity selector device comprising in combination a stationarymagnetizable member, a rotatable magnetizable member rotated by saidsynchronous motor and adapted to periodically form a substantiallyclosed magnetic circuit with said stationary member, primary andsecondary coils mounted on said stationary member in inductive relationwith respect to each other, a half-wave rectifier connected in serieswith said primary coil and with said source of alternating current andadapted to periodically energize said magnetic circuit, and meansresponsive to a predetermined value of current impulses induced in saidsecondary coils for interrupting the circuit of said synchronous motorfor a predetermined time interval suflicient to correct the polarity ofthe rectified direct current voltage. I

HOWARD E. CORBI'IT.

